It's the date that the bottle was made Sam, on your bottle it says a date, in your case 2012/11 (November 2012) a bottle (your type of bottle) will have 15 years of life, and will need testing every 5 years. But as BayBlade says, it's in the photo, I just missed it! Doh!A born date? Would that be on the bottle or is that when it was first used? Sam